The present invention relates to a squeegee device of the type including a squeegee roller for applying a liquid or viscous material to a surface to be treated, in particular for the purpose of screen printing, and a profiled plate arranged in front or upstream of the area of the squeegee roller, the profiled plate forming a guide element for the coating material.
In a known device of this kind (see Austrian Pat. No. 315,800) the profiled plate is in the form of a known type of blade squeegee, so that the roller squeegee arranged behind or downstream thereof is merely employed for pressing the material applied by the blade squeegee into the surface to be treated.
On the other hand, in many printing devices it is necessary that a considerable amount of coating or printing material reach the front or upstream side of the squeegee roller. Until the present time this was always associated with the problem that since a thin squeegee roller can itself support or retain only a very limited aamount of coating material, it was necessary to provide the squeegee roller with a diameter greater than optimal for printing purposes. The capacity of the rotating roller to rotate a sump of coating material exceeding its own height, so that the material does not flow over the roller, is of only limited advantage in this connection. There is also the disadvantage that when the machine is stopped, the material flows into the area behind the squeegee roller, which causes defects in coating when the machine is again started.
Squeegees applied by magnetic pressure produce a completely uniform contact pressure, which is independent of the width of the work. The level of pressure is determined by the magnetic field, the intensity of which is adjustable, and by the available magnetizable mass of the squeegee. The coating roller is freely positioned within the screen or on the material to be colored or coated, and it can be replaced in a simple manner with a roller of a different diameter. The results of the coating operation can be varied by changing the contact pressure and by appropriately selecting the diameter of the squeegee roller. When the force with which the squeegee presses against the base is increased, the coating penetrates the material to a greater depth. A greater amount of coating material can be retained in front of a roller squeegee which has a greater diameter. Accordingly, such squeegees apply greater amounts per unit of surface.
The dependence of the contact pressure and also of the possible size of the sump of material in front or upstream of the squeegee on the diameter of the squeegee roller is a substantial hindrance when the required coating effect is to be obtained by means of roller squeegees of different diameter. Namely, due to the friction and the pressure of the liquid, the squeegee roller is forced from the center of the magnetic field, and in order to maintain the squeegee roller in the coating area, it is necessary to apply a magnetic pressure which is excessive for many kinds of material and coating effects. In order to attain such a contact pressure, a certain magnetizable mass is also required in addition to the field intensity. Accordingly, the use of small diameter roller squeegees is limited. These disadvantages cannot be entirely eliminated, even with the use of known damming plates arranged behind or downstream of the squeegee roller (see Austrian Pat. Nos. 266,024 and 306,750), since the rotating ink sump in front or upstream of the squeegee roller exerts a direct braking force on the squeegee roller and additionally presses against the damming plate with such a force that a braking effect also occurs due to contact between the roller and plate.